XofY OSM Geometry Viewer by Matt Whilden - A web tool for visualizing collections of OpenStreetMap features by type and by city.

Aeris - Realtime 3D flight tracker by kewonit - A 3D flight tracker showing the realtime positions of commercial flights, color-coded by altitude

Land Lines by Zach Lieberman, Matt Felsen, and the Data Arts Team - Draw a line and match it to a satellite image from around the world.

Library of Babel by Jonathan Basile - Comprehensive archive of every possible 3200 character text. Inspired by Jorge Luis Borges